The present invention relates to a miniaturized, low power, programmable x-ray source for use in delivering substantially constant or intermittent levels of x-rays to a specified region. More specifically, the invention relates to apparatus and methods for delivering a uniform x-ray flux to an interior surface of a body cavity.
Most conventional medical x-ray sources are large, fixed position machines. Generally, the head of the x-ray tube is placed in one room and the control console in an adjoining area, with a protective wall, equipped with a viewing window, separating the two. The x-ray tube typically is approximately 20 to 35 centimeters (cm) long, and approximately 15 cm in diameter. A high voltage power supply is housed within a container located in a corner of the room containing the x-ray tube. Patients are brought to the machine for diagnostic, therapeutic, or palliative treatment.
Diagnostic x-ray machines are typically operated at with electron acceleration voltages below 150 kilovolts (kV), and at beam currents from approximately 25 to 1200 milliamps (mA). By contrast, the currents in therapeutic units typically do not exceed 20 mA at voltages which may range above 150 kV. When an x-ray machine is operated at nominal voltages of 10 to 140 kV, the emitted x-rays provide limited penetration of tissue, and are thus useful in treating skin lesions. At higher voltages (approximately 250 kV), deep x-ray penetration is achieved, which is useful in the treatment of major body tumors. Super voltage machines, operable in the 4 to 8 megavolt (MV) region, are used to ablate or destroy all types of tumors, except superficial skin lesions.
One disadvantage of most x-ray devices used for therapy is the high voltage, and consequent high energy radiation, required when directed to soft tissue within or beneath bone. One example is in directing x-rays to areas of the human brain, which is surrounded by bone. High energy x-rays are required to penetrate the bone, but often damage the skin and brain tissue between the radiation entry site and the tumor. Another example in radiation therapy is in directing the x-rays to soft tissue located within the body cavity, couched among other soft tissue, or within an internal calciferous structure. Present high-voltage x-ray machines are limited in their ability to selectively provide desired x-ray radiation to such areas.
Another disadvantage of conventional high voltage sources is the damage caused to skin external to the affected organ or tissue. Therefore, prior art high voltage x-ray sources often cause significant damage not only to the target region or tissue, but also to all tissue between the entry site, the target region, and the exit site, particularly when used for human tumor therapy. However, since present devices apply x-ray radiation to target regions internal to a patient from a source external to the target region, such incidental tissue damage is practically unavoidable.
Conventional radiation therapy treatment of the soft tissue that lines body cavities, such as the bladder, vagina and cervix, urethra, uterus, colon, and rectum, involves application of x-radiation from an extra-corporal source. Consequently, such techniques of radiation therapy have the disadvantage that they necessarily radiate areas of the patient between the radiation entry site, the target tissue, and the exit site, causing damage to such tissue.
Conventional methods of radiation treatment for body cavities also have the further disadvantage of failing to provide the ability to establish a uniform dose of radiation to the target tissue. In some cases, it is desirable that radiation treatment of the tissue lining a body cavity provide the same dose of radiation to every segment of the tissue, i.e., a uniform dose. In other cases, specifically contoured non-uniform doses may be desired. The prior art x-ray sources cannot accomplish this for interior body cavities. As used herein, the term "uniform dose" refers to an isodose contour, i.e., a surface over which the flux density is substantially constant.
Some of these disadvantages can be overcome through the use of miniaturized low power x-ray sources, such as the one described in U.S. Pat. No. 5,153,900 issued to Nomikos et al. which is hereby incorporated by reference. These sources can be inserted into, and activated from within, a patient's body. Thus, these sources can generate x-rays local to the target tissue. When such x-ray sources are used to treat the tissue lining a body cavity, the x-rays need not pass through the patient's skin, bone and other tissue prior to reaching the target tissue. However, even utilizing these sources it is difficult to provide a uniform, or other desired, dose of radiation to the target tissue, particularly where the geometry of the target region is not fixed, for example, as in the bladder which has a flexible inner wall without a well-defined shape.
By way of example, some x-ray sources generally of the type disclosed in U.S. Pat. No. 5,153,900 act as point sources of x-ray radiation. Therefore, the strength of the radiation field decreases uniformly in air with approximately the square of the distance from the source (i.e., 1/R.sup.2). Since body cavities are not generally spherically symmetrical, a point source within a body cavity will not deliver a uniform dose of radiation to the tissue lining the cavity.
It is therefore an object of the invention to provide a method and apparatus for delivering a uniform, or other desired, dose of radiation to the tissue that lines a body cavity.
It is a further object of the invention to provide an apparatus, that includes a miniature low power x-ray source, for delivering a uniform, or other desired, dose of radiation to the tissue that lines a body cavity.
Other objects and advantages of the present invention will become apparent upon consideration of the appended drawings and description thereof.